1. Field of the Invention
The present invention relates generally to internal combustion engines and in particular to apparatus for vaporizing fuel/air aerosol mixtures produced by carburetors.
2. Description of the Prior Art
In an internal combustion engine, the function of the carburetor is to produce a combustible fuel-and-air mixture. The combustible mixture may comprise an aerosol mixture of tiny droplets of fuel entrained in a stream of air, or it may be a homogeneous mixture of vaporized fuel and air. In carburetors which produce an aerosol mixture, fuel is aspirated in a stream of combustion air with the assistance of a venturi. As a result of heat absorption on the way to the cylinder, these droplets are vaporized, so that the mixture thus becomes a flammable gas. The efficiency of the engine is directly related to the amount of energy released by combustion of a given volume of fuel/air mixture within the cylinder. The primary purpose of the conventional carburetor is to mix the fuel droplets uniformly with intake air in the proper proportions to produce a uniform aerosol mixture with the goal of obtaining complete combustion.
In the operation of conventional carburetors, liquid fuel is aspirated from a choke tube by the suction developed within a venturi region of the carburetor air passage. The aspiration of the fuel within this relatively low pressure region causes the fuel to be finely divided into tiny droplets that are carried along in a moving air mass to the cylinder. The size of each fuel droplet produced for a given pressure and air flow rate is dependent upon the viscosity of the fuel, and the viscosity of the fuel is dependent upon its temperature. It will be appreciated that at relatively low temperatures, the fuel droplets will be larger and will be less uniformly distributed throughout the moving air mixture, thereby leading to incomplete combustion when introduced into the cylinder. Conversely, it will also be appreciated that as the temperature of the fuel is increased, the fuel droplets constantly diminish in size until fuel vapor is produced. The reason for this is that the surface tension of the fuel droplets increases as fuel temperature decreases.
It is well known that a liquid fuel may be heated and converted to a vapor for mixture with air to establish a combustible fuel/air mixture for delivery to the combustion chamber of an internal combustion engine. By vaporizing the liquid fuel, the mixing takes place prior to entering the intake manifold, affording rapid, efficient ignition in the combustion chamber. However, for high flow rates of combustion air, it is difficult to maintain the appropriate fuel/air ratio over the wide operating range from idle through cruise and high speed operation. The most common problem involved in such arrangements is that the fuel/air ratio is too lean, resulting in higher than normal engine operating temperatures. Widespread use of such fuel preheater arrangements has been limited by the fuel vapor volume requirements for carburetors having relatively high flow rates of combustion air, and the inability to mix the preheated fuel vapor with the incoming air in the correct proportions to satisfy a wide range of engine operating conditions.
In the conventional carburetor, liquid fuel is mixed with incoming air and flows to the combustion chamber as a wet aerosol mist through the intake manifold. A large percentage of fuel droplets coat the intake manifold or combustion chamber walls and are blown into the exhaust manifold due to intake-exhaust overlap. The combustion reaction takes place when a molecule of oxygen links with a similar molecule of fuel by coupling of the outer rings. This coupling can only be accomplished when the fuel and oxidizer have been vaporized to a dry gas. A liquid fuel droplet can only vaporize on the interfacing surface with the oxidizer. Energy released is greatly restricted, and because of the high temperatures associated combustion, the liquid fuel which does not burn forms nitrousoxides and hydrocarbon waste products which gives rise to air pollution. Preferably, the fuel/air mixture is completely vaporized inside the intake manifold, thereby permitting instantaneous, efficient ignition in the combustion chamber.
Accordingly, there is a continuing interest in providing a carburetor and fuel preheater combination having the ability to produce an adequate volume of fuel vapor and having the ability to mix the fuel vapor with incoming air in the correct proportions to satisfy a wide range of engine operating conditions, and also to preheat the fuel/air mixture to provide efficient ignition and combustion within the engine cylinders.
Because more complete combustion and substantially more energy can be derived from a given volume of fuel/air aerosol mixture in which the droplets of fuel are very finely divided and uniformly dispersed, as opposed to the same volume of air mixed with superheated fuel vapor, it is desirable to maintain the temperature of the fuel substantially below its boiling point during the time that the fuel/air aerosol mixture is produced.